Harry has taken legal action against a number of newspaper publishers.
London CNN  — 

Prince Harry will take to the witness stand Tuesday as his years-long battle against Britain’s tabloid media reaches its most dramatic stage so far.

The royal is preparing to face questions in a London court as part of his case against a major newspaper publisher. But the judge in the case said he was “a little surprised” at Harry’s failure to show up at court on Monday for the latest hearing in the Duke of Sussex’s case against Mirror Group Newspapers (MGN).

Harry arrived in the UK on Sunday night after catching a flight from Los Angeles, Prince Harry’s lawyer David Sherborne said in court on Monday. According to Sherborne, Harry attended his daughter’s birthday on Sunday.

The appearance of a British royal in a witness box will be an exceptionally rare event. But Harry has long railed against the tactics of the tabloid media in covering his life, and he will now have the opportunity to lay out his arguments, under oath, during cross-examination from MGN’s lawyers.

It’s likely to be a tense and defining appearance for the Duke as he forges his own path further from the rest of the royal family.

Here’s what you need to know about the trial.

What is the case about?

The Duke of Sussex and three other claimants representing dozens of celebrities are suing MGN, accusing its titles of obtaining private information by phone hacking and through other illicit means, including private investigators, between 1991 and 2011.

The trial started on May 10, and is expected to last seven weeks.

MGN is contesting most of the allegations, arguing in its court filings that some claims have been brought too late and that in all four cases there is insufficient evidence of phone hacking.

In court documents published last month, the publisher did apologize for one instance of unlawful information gathering nearly 20 years ago. That incident involved a private investigator, who was paid £75 ($95) in 2004 by the Sunday People, a tabloid owned by the same group, to gather information about the Duke of Sussex while at a London nightclub.

Harry’s lawyer David Sherborne has said his claim against MGN, which covers incidences from 1995 to 2011, is “significant not just in terms of time span but in the range of activity it covers.”

Harry was subject to the most “intrusive methods of obtaining personal information,” Sherborne said, arguing that “no one should be subjected to that.” The “unlawful methods” were “habitual and widespread” among the journalists, Sherborne added.

What happened on Monday?

A huge crowd of media gathered outside the doors to the High Court on Monday morning, hoping for a glimpse of the Duke – whom it was later revealed won’t be present until Tuesday.

Inside the court, Sherborne laid out parts of Harry’s case, introducing some of the articles that will be considered at the trial.

The barrister said that unlawful activities to gather information “acted like a web” around Harry and took place “beneath the radar” at MGN newspapers, according to the PA Media news agency.

The first article, from September 1996, was headlined “Diana so sad on Harry’s big day,” and detailed a visit from Princess Diana to see Harry on his 12th birthday, according to PA Media. MGN denies was the result of unlawful activity and argues the information was in the public domain already, PA reported.

Another story discussed touched on the relationship between Harry and Prince William in 2003.

What will Harry say?

When Harry enters the witness box on Tuesday he can expect a tough examination from the publisher’s lawyers.

The prince alleges that about 140 articles published in titles belonging to the group contained information gathered using unlawful methods, and 33 of those articles have been selected to be considered at the trial, according to PA Media.